Direct smelting process and apparatus

ABSTRACT

A molten-bath based direct smelting process and apparatus for producing metals from a ferrous material is disclosed. The process includes injecting feed materials being solid material and carrier gas into a molten bath at a velocity of at least 40 m/s through at least one downwardly extending solids injection lance having a delivery tube of internal diameter of 40–200 mm that is located so that a central axis of an outlet end of the lance is at an angle of 20 to 90 degrees to a horizontal axis. The feed materials injection generates a superficial gas flow of at least 0.04 Nm 3 /s/m 2  within the molten bath at least in part by reactions of injected material in the bath. The gas now causes molten material to be projected upwardly as splashes, droplets and streams and form an expanded molten bath zone, with the gas flow and the upwardly projected molten material causing substantial movement of material within the molten bath and strong mixing of the molten bath. The feed materials are selected so that, in an overall sense, the reactions of the feed materials in the molten bath are endothermic. The process also includes injecting an oxygen-containing gas into an upper region of the vessel via at least one oxygen gas injection lance and post-combusting combustible gases released from the molten bath.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process and an apparatus forproducing molten metal (which term includes metal alloys), in particularalthough by no means exclusively iron, from ferrous material, such asores, partly reduced ores and metal-containing waste streams.

The present invention relates particularly to a molten metal bath-baseddirect smelting process and an apparatus for producing molten metal froma ferrous material.

2. Description of Related Art

One known molten bath-based direct smelting process for producing moltenferrous metal is the DIOS process. The DIOS process includes apre-reduction stage and a smelt reduction stage. In the DIOS process ore(−8 mm) is pre-heated (750° C.) and pre-reduced (10 to 30%) in fluidisedbeds using offgas from a smelt reduction vessel which contains a moltenbath of metal and slag, with the slag forming a deep layer on the metal.The fine (−3 mm) and coarse (−8 mm) components of the ore are separatedin the pre-reduction stage of the process. Coal and pre-heated andpre-reduced ore (via two feed lines) are fed continuously into the smeltreduction furnace from the top of the furnace. The ore dissolves andforms FeO in the deep layer of slag and the coal decomposes into charand volatile matter in the slag layer. Oxygen is blown through aspecially designed lance that improves secondary combustion in thefoamed slag. Oxygen jets burn carbon monoxide that is generated with thesmelting reduction reactions, thereby generating heat that istransferred to the molten slag. The FeO is reduced at the slag/metal andslag/char interfaces. Stirring gas introduced into the hot metal bathfrom the bottom of the smelt reduction vessel improves heat transferefficiency and increases the slag/metal interface for reduction. Slagand metal are tapped periodically.

Another known direct smelting process for producing molten ferrous metalis the AISI process. The AISI process also includes a pre-reductionstage and a smelt reduction stage. In the AISI process pre-heated andpartially pre-reduced iron ore pellets, coal or coke breeze and fluxesare top charged into a pressurised smelt reactor which contains a moltenbath of metal and slag. The coal devolatilises in the slag layer and theiron ore pellets dissolve in the slag and then are reduced by carbon(char) in the slag. The process conditions result in slag foaming.Carbon monoxide and hydrogen generated in the process are post combustedin or just above the slag layer to provide the energy required for theendothermic reduction reactions. Oxygen is top blown through a central,water cooled lance and nitrogen is injected through tuyeres at thebottom of the reactor to ensure sufficient stirring to facilitate heattransfer of the post combustion energy to the bath. The process offgasis de-dusted in a hot cyclone before being fed to a shaft type furnacefor pre-heating and pre-reduction of the pellets to FeO or wustite.

Another known direct smelting process, which relies on a molten metallayer as a reaction medium, and is generally referred to as the HIsmeltprocess, is described in International application PCT/AU96/00197 (WO96/31627) in the name of the applicant.

The HIsmelt process as described in the International applicationcomprises:

-   -   (a) forming a bath of molten metal and slag in a vessel;    -   (b) injecting into the bath:        -   (i) metalliferous feed material, typically metal oxides; and        -   (ii) a solid carbonaceous material, typically coal, which            acts as a reductant of the metal oxides and a source of            energy; and    -   (c) smelting the metalliferous feed material to metal in the        metal layer.

The HIsmelt process also comprises injecting oxygen-containing gas intoa space above the bath and post-combusting reaction gases, such as COand H₂, released from the bath and transferring the heat generated tothe bath to contribute to the thermal energy required to smelt themetalliferous feed materials.

The HIsmelt process also comprises forming a transition zone in thespace above the nominal quiescent surface of the bath in which there isa favourable mass of ascending and thereafter descending droplets orsplashes or streams of molten materiel which provide an effective mediumto transfer to the bath the thermal energy generated by post-combustingreaction gases above the bath.

The HIsmelt process as described in the international application ischaracterised by forming the transition zone by injecting a carrier gas,metalliferous feed material, and solid carbonaceous material into thebath through a section of the side of the vessel that is in contact withthe bath and/or from above the bath so that the carrier gas and thesolid material penetrate the bath and cause molten material to beprojected into the space above the surface of the bath.

The HIsmelt process as described in the International application is animprovement over earlier forms of the HIsmelt process which form thetransition zone by bottom injection of gas and/or carbonaceous materialinto the bath which causes droplets and splashes and streams of moltenmaterial to be projected from the bath.

SUMMARY OF THE INVENTION

The applicant has carried out extensive research and pilot plant work ondirect smelting processes and has made a series of significant findingsin relation to such processes.

In general terms, the present invention provides a direct smeltingprocess for producing metals (which term includes metal alloys) from aferrous material which includes the steps of:

-   -   (a) forming a bath of molten metal and molten slag in a        metallurgical vessel;    -   (b) injecting feed materials being solid material and carrier        gas into the molten bath at a velocity of at least 40 m/s        through a downwardly extending solids injection lance having a        delivery tube of internal diameter of 40–200 mm that is located        so that a central axis of an outlet end of the lance is at an        angle of 20 to 90 degrees to a horizontal axis and generating a        superficial gas flow of at least 0.04 Nm³/s/m² within the molten        bath (where m² relates to the area of a horizontal cross-section        through the molten bath) at least in part by reactions of        injected material in the bath which causes molten material to be        projected upwardly as splashes, droplets and streams and form an        expanded molten bath zone, the gas flow and the upwardly        projected molten material causing substantial movement of        material within the molten bath and strong mixing of the molten        bath, the feed materials being selected so that, in an overall        sense, the reactions of the feed materials in the molten bath        are endothermic; and    -   (c) injecting an oxygen-containing gas into an upper region of        the vessel via at least one oxygen gas injection lance and        post-combusting combustible gases released from the molten bath,        whereby ascending and thereafter descending molten material in        the expanded molten bath zone facilitate heat transfer to the        molten bath.

The expanded molten bath zone is characterised by a high volume fractionof gas voidages throughout the molten material.

Preferably the volume fraction of gas voidages is at least 30% by volumeof the expanded molten bath zone.

The splashes, droplets and streams of molten material are generated bythe above-described flow of gas within the molten bath. Whilst theapplicant does not wish to be bound by the following comments, theapplicant believes that the splashes, droplets and streams are generatedby a churn-turbulent regime at lower gas flow rates and by a fountainregime at higher gas flow rates.

Preferably the gas flow and the upwardly projected molten material causesubstantial movement of material into and from the molten bath.

Preferably the solid material includes ferrous material and/or solidcarbonaceous material.

The above-described expanded molten bath zone is quite different to thelayer of foaming slag produced in the above-described AISI process.

Preferably step (b) includes injecting feed materials into the moltenbath so that the feed materials penetrate a lower region of the moltenbath.

Preferably the expanded molten bath zone forms on the lower region ofthe molten bath.

Preferably step (b) includes injecting feed materials into the moltenbath via the lance at a velocity in the range of 80–100 m/s.

Preferably step (b) includes injecting feed materials into the moltenbath via the lance at a mass flow rate of up to 2.0 t/m²/s where m²relates to the cross-sectional area of the lance delivery tube.

Preferably step (b) includes injecting feed materials into the moltenbath via the lance at a solids/gas ratio of 10–25 kg solids/Nm³ gas.

More preferably the solid gas ratio is 10–18 kg solids/Nm³ gas.

Preferably the gas flow within the molten bath generated in step (b) isat least 0.04 Nm³/s/m² at the quiescent surface of the molten bath.

More preferably the gas flow within the molten bath is at a flow rate ofat least 0.2 Nm³/s/m².

More preferably the gas flow rate is at least 0.3 Nm³/s/m².

Preferably the gas flow rate is less than 2 Nm³/s/m².

The gas flow within the molten bath may be generated in part as a resultof bottom and/or side wall injection of a gas into the molten bath,preferably the lower region of the molten bath.

Preferably the oxygen-containing gas is air or oxygen-enriched air.

Preferably the process includes injecting air or oxygen-enriched airinto the vessel at a temperature of 800–1400° C. and at a velocity of200–600 m/s via at least one oxygen gas injection lance and forcing theexpanded molten bath zone in the region of the lower end of the lanceaway from the lance and forming a “free” space around the lower end ofthe lance that has a concentration of molten material that is lower thanthe molten material concentration in the expanded molten bath zone; thelance being located so that: (i) a central axis of the lance is at anangle of 20 to 90° relative to a horizontal axis; (ii) the lance extendsinto the vessel a distance that is at least the outer diameter of thelower end of the lance; and (iii) the lower end of the lance is at least3 times the outer diameter of the lower end of the lance above thequiescent surface of the molten bath.

Preferably the concentration of molten material in the free space aroundthe lower end of the lance is 5% or less by volume of the space.

Preferably the free space around the lower end of the lance is asemi-spherical volume that has a diameter that is at least 2 times theouter diameter of the lower end of the lance.

Preferably the free space around the lower end of the lance is no morethan 4 times the outer diameter of the lower end of the lance.

Preferably at least 50%, more preferably at least 60%, by volume of theoxygen in the air or oxygen enriched air is combusted in the free spacearound the lower end of the lance.

Preferably the process includes injecting air or oxygen-enriched airinto the vessel in a swirling motion.

The term “smelting” is understood herein to mean thermal processingwherein chemical reactions that reduce the ferrous feed material takeplace to produce liquid metal.

The term “quiescent surface” in the context of the molten bath isunderstood to mean the surface of the molten bath under processconditions in which there is no gas/solids injection and therefore nobath agitation.

Preferably the process includes maintaining a high slag inventory in thevessel relative to the molten ferrous metal in the vessel.

The amount of slag in the vessel, ie the slag inventory, has a directimpact on the amount of slag that is in the expanded molten bath zone.

The relatively low heat transfer characteristics of slag compared tometal is important in the context of minimising heat loss from theexpanded molten bath zone to the water cooled side walls and from thevessel via the side walls of the vessel.

By appropriate process control, slag in the expanded molten bath zonecan form a layer or layers on the side walls that adds resistance toheat loss from the side walls.

Therefore, by changing the slag inventory it is possible to increase ordecrease the amount of slag in the expanded molten bath zone and on theside walls and therefore control the heat loss via the side walls of thevessel.

The slag may form a “wet” layer or a “dry” layer on the side walls. A“wet” layer comprises a frozen layer that adheres to the side walls, asemi-solid (mush) layer, and an outer liquid film. A “dry” layer is onein which substantially all of the slag is frozen.

The amount of slag in the vessel also provides a measure of control overthe extent of post combustion.

Specifically, if the slag inventory is too low there will be increasedexposure of metal in the expanded molten bath zone and thereforeincreased oxidation of metal and dissolved carbon in metal and thepotential for reduced post-combustion and consequential decreased postcombustion, notwithstanding the positive effect that metal in theexpanded molten bath zone has on heat transfer to the metal layer.

In addition, if the slag inventory is too high the one or more than oneoxygen-containing gas injection lance/tuyere will be buried in theexpanded molten bath zone and this minimises movement of top spacereaction gases to the end of the or each lance/tuyere and, as aconsequence, reduces potential for post-combustion.

The amount of slag in the vessel, ie the slag inventory, may becontrolled by the tapping rates of metal and slag.

The production of slag in the vessel may be controlled by varying thefeed rates of metalliferous feed material, carbonaceous material, andfluxes to the vessel and operating parameters such as oxygen-containinggas injection rates.

Preferably the process includes controlling the level of dissolvedcarbon in molten iron to be at least 3 wt % and maintaining the slag ina strongly reducing condition leading to FeO levels of less than 6 wt %,more preferably less than 5 wt %, in the slag.

Preferably ferrous material is smelted to metal at least predominantlyin the lower region of the molten bath. Invariably, this region of thevessel is where there will be a high concentration of metal.

In practice, there will be a proportion of the ferrous material that issmelted to metal in other regions of the vessel. However, the objectiveof the process of the present invention, and an important differencebetween the process and prior art processes, is to maximise smelting offerrous material in the lower region of the molten bath.

Step (b) of the process may include injecting feed materials through aplurality of solids injection lances and generating the gas flow of atleast 0/04 Nm³/s/m² within the molten bath.

The injection of ferrous material and carbonaceous material may bethrough the same or separate lances.

Preferably the process includes causing molten material to be projectedabove the expanded molten bath zone.

Preferably the level of post-combustion is at least 40%, wherepost-combustion is defined as:$\frac{\left\lbrack {CO}_{2} \right\rbrack + \left\lbrack {H_{2}O} \right\rbrack}{\left\lbrack {CO}_{2} \right\rbrack + \left\lbrack {H_{2}O} \right\rbrack + \lbrack{CO}\rbrack + \left\lbrack H_{2} \right\rbrack}$

where:

[CO₂]=volume % of CO₂ in off-gas

[H₂O]=volume % of H₂O in off-gas

[CO]=volume % of CO in off-gas

[H₂]=volume % of H₂ in off-gas

The expanded molten bath zone is important for 2 reasons.

Firstly, the ascending and thereafter descending molten material is aneffective means of transferring to the molten bath the heat generated bypost-combustion of reaction gases.

Secondly, the molten material, and particularly the slag, in theexpanded molten bath zone is an effective means of minimising heat lossvia the side walls of the vessel.

An important difference between the preferred embodiment of the processof the present invention and prior art processes is that in thepreferred embodiment the main smelting region is the lower region of themolten bath and the main oxidation (ie heat generation) region is aboveand in an upper region of the expanded molten bath zone and theseregions are spatially well separated and heat transfer is via physicalmovement of molten metal and slag between the two regions.

According to the present invention there is also provided an apparatusfor producing metal from a ferrous material by a direct smeltingprocess, which apparatus includes a fixed non-tiltable vessel thatcontains a molten bath of metal and slag and includes a lower region andan expanded molten bath zone above the lower region, the expanded moltenbath zone being formed by gas flow from the lower region which carriesmolten material upwardly from the lower region, which vessel includes:

-   -   (a) a hearth formed of refractory material having a base and        sides in contact with the lower region of the molten bath;    -   (b) side walls extending upwardly from the sides of the hearth        and being in contact with an upper region of the molten bath and        the gas continuous space, wherein the side walls that contact        the gas continuous space include water cooled panels and a layer        of slag on the panels;    -   (c) at least one lance extending downwardly into the vessel and        injecting oxygen-containing gas into the vessel above the molten        bath;    -   (d) at least one lance injecting feed materials being ferrous        material and/or carbonaceous material and carrier gas into the        molten bath at a velocity of at least 40 m/s, the lance being        located so that a central axis of an outlet end of the lance is        angled downwardly at an angle of 20 to 90° to a horizontal axis,        the lance having a delivery tube for injecting feed materials        which has an internal diameter of 40–200 mm; and    -   (e) a means for tapping molten metal and slag from the vessel.

Preferably the feed material injection lance is located so that theoutlet end of the lance is 150–1500 mm above the nominal quiescentsurface of a metal layer of the molten bath.

Preferably the feed materials injection lance includes a central coretube through which to pass the solid particulate material; an annularcooling jacket surrounding the central core tube throughout asubstantial part of its length, which jacket defines an inner elongateannular water flow passage disposed about the core tube, an outerelongate annular water flow passage disposed about the inner water flowpassage, and an annular end passage interconnecting the inner and outerwater flow passages at a forward end of the cooling jacket; water inletmeans for inlet of water into the inner annular water flow passage ofthe jacket at a rear end region of the jacket; an water outlet means foroutlet of water from the outer annular water flow passage at the rearend region of the jacket, whereby to provide for flow of cooling waterforwardly along the inner elongate annular passage to the forward end ofthe jacket then through the end flow passage means and backwardlythrough the outer elongate annular water flow passage, wherein theannular end passage curves smoothly outwardly and backwardly from theinner elongate annular passage to the outer elongate annular passage andthe effective cross-sectional area for water flow through the endpassage is less than the cross-sectional flow areas of both the innerand outer elongate annular water flow passages.

The present invention is described further by way of example withreference to the accompanying drawings of which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical section illustrating in schematic form a preferredembodiment of the process and the apparatus of the present invention;

FIGS. 2A and 2B join on the line A—A to form a longitudinalcross-section through one of the solids injection lances shown in FIG.1;

FIG. 3 is an enlarged longitudinal cross-section through a rear end ofthe lance;

FIG. 4 is an enlarged cross-section through the forward end of thelance; and

FIG. 5 is a transverse cross-section on the line 5—5 in FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is in the context of smelting iron ore toproduce molten iron and it is understood that the present invention isnot limited to this application and is applicable to any suitableferrous ores and/or concentrates—including partially reduced metallicores and waste revert materials.

The direct smelting apparatus shown in FIG. 1 includes a metallurgicalvessel denoted generally as 11. The vessel 11 has a hearth that incudesa base 12 and sides 13 formed from refractory bricks; side walls 14which form a generally cylindrical barrel extending upwardly from thesides 13 of the hearth and which includes an upper barrel section formedfrom water cooled panels (not shown) and a lower barrel section formedfrom water cooled panels (not shown) having an inner lining ofrefractory bricks; a roof 17; an outlet 18 for off-gases; a forehearth19 for discharging molten metal continuously; and a tap-hole 21 fordischarging molten slag.

In use, under quiescent conditions, the vessel contains a molten bath ofiron and slag which includes a layer 22 of molten metal and a layer 23of molten slag on the metal layer 22.

The term “metal layer” is understood herein to mean that region of thebath that is predominantly metal.

The space above the nominal quiescent surface of the molten bath ishereinafter referred to as the “top space”.

The arrow marked by the numeral 24 indicates the position of the nominalquiescent surface of the metal layer 22 and the arrow marked by thenumeral 25 indicates the position of the nominal quiescent surface ofthe slag layer 23 (ie of the molten bath).

The term “quiescent surface” is understood to mean the surface whenthere is no injection of gas and solids into the vessel.

The vessel is fitted with a downwardly extending hot air injection lance26 for delivering a hot air blast into an upper region of the vessel andpost-combusting reaction gases released from the molten bath. The lance26 has an outer diameter D at a lower end of the lance. The lance 26 islocated so that:

-   -   (i) a central axis of the lance 26 is at an angle of 20 to 90°        relative to a horizontal axis (the lance 26 shown in FIG. 1 is        at an angle of 90°);    -   (ii) the lance 26 extends into the vessel a distance that is at        least the outer diameter D of the lower end of the lance; and    -   (iii) the lower end of the lance 26 is at least 3 times the        outer diameter D of the lower end of the lance above the        quiescent surface 25 of the molten bath.

The vessel is also fitted with solids injection lances 27 (two shown)extending downwardly and inwardly through the side walls 14 and into themolten bath with outlet ends 82 of the lances 27 at an angle of 20–70°to the horizontal for injecting iron ore, solid carbonaceous material,and fluxes entrained in an oxygen-deficient carrier gas into the moltenbath. The position of the lances 27 is selected so that their outletends 82 are above the quiescent surface 24 of the metal layer 22. Thisposition of the lances 27 reduces the risk of damage through contactwith molten metal and also makes it possible to cool the lances 27 byforced internal water cooling without significant risk of water cominginto contact with the molten metal in the vessel. Specifically, theposition of the lances 27 is selected so that the outlet ends 82 are inthe range of 150–1500 mm above the quiescent surface 24 of the metallayer 22. In this connection, it is noted that, whilst the lances 27 areshown in FIG. 1 as extending into the vessel, the outlet ends of thelances 27 may be flush with the side wall 14. The lances 27 aredescribed in more detail with reference to FIGS. 2–5.

In use, iron ore, solid carbonaceous material (typically coal), andfluxes (typically lime and magnesia) entrained in a carrier gas(typically N₂) are injected into the molten bath via the lances 27 at avelocity of at least 40 m/s, preferably 80–100 m/s. The momentum of thesolid material/carrier gas causes the solid material and gas topenetrate to a lower region of the molten bath. The coal isdevolatilised and thereby produces gas in the lower bath region. Carbonpartially dissolves into the metal and partially remains as solidcarbon. The iron ore is smelted to metal and the smelting reactiongenerates carbon monoxide gas. The gases transported into the lower bathregion and generated via devolatilisation and smelting producesignificant buoyancy uplift of molten metal, solid carbon, and slag(drawn into the lower bath region as a consequence ofsolid/gas/injection) from the lower bath region which generates anupward movement of splashes, droplets and streams of molten metal andslag, and these splashes, and droplets, and streams entrain slag as theymove through an upper region of the molten bath. The gas flow generatedby the above-described injection of carrier gas and bath reactions is atleast 0.04 Nm³/s/m² of the quiescent surface of the molten bath (ie thesurface 25).

The buoyancy uplift of molten metal, solid carbon and slag causessubstantial agitation in the molten bath, with the result that themolten bath expands in volume and forms an expanded molten bath zone 28that has a surface indicated by the arrow 30. The extent of agitation issuch that there is substantial movement of molten material within themolten bath (including movement of molten material into and from thelower bath region) and strong mixing of the molten bath to the extentthat there is reasonably uniform temperature throughout the moltenbath—typically, 1450–1550° C. with a temperature variation of the orderof 30° in each region.

In addition, the upward gas flow projects some molten material(predominantly slag) beyond the expanded molten bath zone 28 and ontothe part of the upper barrel section of the side walls 14 that is abovethe expanded molten bath zone 28 and onto the roof 17.

In general terms, the expanded molten bath zone 28 is a liquidcontinuous volume, with gas bubbles therein.

In addition to the above, in use, hot air at a temperature of 800–1400°C. is discharged at a velocity of 200–600 m/s via lance 26 andpenetrates the central region of the expanded molten bath zone 28 andcauses an essentially metal/slag free space 29 to form around the end ofthe lance 26.

The hot air blast via the lance 26 post-combusts reaction gases CO andH₂ in the expanded molten bath zone 28 and in the free space 29 aroundthe end of the lance 26 and generates high temperatures of the order of2000° C. or higher in the gas space. The heat is transferred to theascending and descending splashes droplets, and streams, of moltenmaterial in the region of gas injection and the heat is then partiallytransferred throughout the molten bath.

The free space 29 is important to achieving high levels of postcombustion because it enables entrainment of gases in the space abovethe expanded molten bath zone 28 into the end region of the lance 26 andthereby increases exposure of available reaction gases to postcombustion.

The combined effect of the position of the lance 26, gas flow ratethrough the lance 26, and upward movement of splashes, droplets andstreams of molten material is to shape the expanded molten bath zone 28around the lower region of the lance 26. This shaped region provides apartial barrier to heat transfer by radiation to the side walls 14.

Moreover, the ascending and descending droplets, splashes and streams ofmolten material is an effective means of transferring heat from theexpanded molten bath zone 28 to the molten bath with the result that thetemperature of the zone 28 in the region of the side walls 14 is of theorder of 1450° C.–1550° C.

The construction of the solids injection lances is illustrated in FIGS.2 to 5.

As shown in these figures, each lance 27 comprises a central core tube31 through which to deliver the solids material and an annular coolingjacket 32 surrounding the central core tube 31 throughout a substantialpart of its length. Central core tube 31 is formed of carbon/alloy steeltubing 33 throughout most of its length, but a stainless steel section34 at its forward end projects as a nozzle from the forward end ofcooling jacket 32. The forward end part 34 of core tube 31 is connectedto the carbon/alloy steel section 33 of the core tube through a shortsteel adaptor section 35 which is welded to the stainless steel section34 and connected to the carbon/alloy steel section through a screwthread 36.

Central core tube 31 is internally lined through to the forward end part34 with a thin ceramic lining 37 formed by a series of cast ceramictubes. The rear end of the central core tube 31 is connected through acoupling 38 to a T-piece 39 through which particulate solids material isdelivered in a pressurised fluidising gas carrier, for example nitrogen.

Annular cooling jacket 32 comprises a long hollow annular structure 41comprised of outer and inner tubes 42, 43 interconnected by a front endconnector piece 44 and an elongate tubular structure 45 which isdisposed within the hollow annular structure 41 so as to divide theinterior of structure 41 into an inner elongate annular water flowpassage 46 and an outer elongate annular water flow passage 47. Elongatetubular structure 45 is formed by a long carbon steel tube 48 welded toa machined carbon steel forward end piece 49 which fits within the frontend connector 44 of the hollow tubular structure 41 to form an annularend flow passage 51 which interconnects the forward ends of the innerand outer water flow passages 46, 47.

The rear end of annular cooling jacket 32 is provided with a water inlet52 through which the flow of cooling water can be directed into theinner annular water flow passage 46 and a water outlet 53 from whichwater is extracted from the outer annular passage 47 at the rear end ofthe lance. Accordingly, in use of the lance cooling water flowsforwardly down the lance through the inner annular water flow passage 46then outwardly and back around the forward annular end passage 51 intothe outer annular passage 47 through which it flows backwardly along thelance and out through the outlet 53. This ensures that the coolest wateris in heat transfer relationship with the incoming solids material toensure that this material does not melt or burn before it dischargesfrom the forward end of the lance and enables effective cooling of boththe solids material being injected through the central core of the lanceas well as effective cooling of the forward end and outer surfaces ofthe lance.

The outer surfaces of the tube 42 and front end piece 44 of the hollowannular structure 41 are machined with a regular pattern of rectangularprojecting bosses 54 each having an undercut or dove tail cross-sectionso that the bosses are of outwardly diverging formation and serve askeying formations for solidification of slag on the outer surfaces ofthe lance. Solidification of slag on to the lance assists in minimisingthe temperatures in the metal components of the lance. It has been foundin use that slag freezing on the forward or tip end of the lance servesas a base for formation of an extended pipe of solid material serving asan extension of the lance which further protects exposure of the metalcomponents of the lance to the severe operating conditions within thevessel.

It has been found that it is very important to cooling of the tip end ofthe lance to maintain a high water flow velocity around the annular endflow passage 51. In particular it is most desirable to maintain a waterflow velocity in this region of the order of 10 meters per second toobtain maximum heat transfer. In order to maximise the water flow ratein this region, the effective cross-section for water flow throughpassage 51 is significantly reduced below the effective cross-section ofboth the inner annular water flow passage 46 and the outer water flowpassage 47. Forward end piece 49 of the inner tubular structure 45 isshaped and positioned so that water flowing from the forward end ofinner annular passage 46 passes through an inwardly reducing or taperednozzle flow passage section 61 to minimise eddies and losses beforepassing into the end flow passage 51. The end flow passage 51 alsoreduces in effective flow area in the direction of water flow so as tomaintain the increased water flow velocity around the bend in thepassage and back to the outer annular water flow passage 47. In thismanner, it is possible to achieve the necessary high water flow rates inthe tip region of the cooling jacket without excessive pressure dropsand the risk of blockages in other parts of the lance.

In order to maintain the appropriate cooling water velocity around thetip end passage 51 and to minimise heat transfer fluctuations, it iscritically important to maintain a constant controlled spacing betweenthe front end piece 49 tubular structure 45 and the end piece 44 of thehollow annular structure 41. This presents a problem due to differentialthermal expansion and contraction in the components of the lance. Inparticular, the outer tube part 42 of hollow annular structure 41 isexposed to much higher temperatures than the inner tube part 43 of thatstructure and the forward end of that structure therefore tends to rollforwardly in the manner indicated by the dotted line 62 in FIG. 4. Thisproduces a tendency for the gap between components 44, 49 defining thepassage 51 to open when the lance is exposed to the operating conditionswithin the smelting vessel. Conversely, the passage can tend to close ifthere is a drop in temperature during operation. In order to overcomethis problem the rear end of the inner tube 43 of hollow annularstructure 41 is supported in a sliding mounting 63 so that it can moveaxially relative to the outer tube 42 of that structure, the rear end ofinner tubular structure 45 is also mounted in a sliding mounting 64 andis connected to the inner tube 43 of structure 41 by a series ofcircumferentially spaced connector cleats 65 so that the tubes 43 and 45can move axially together. In addition, the end pieces 44, 49 of thehollow annular structure 41 and tubular structure 45 are positivelyinterconnected by a series of circumferentially spaced dowels 70 tomaintain the appropriate spacing under both thermal expansion andcontraction movements of the lance jacket.

The sliding mounting 64 for the inner end of tubular structure 45 isprovided by a ring 66 attached to a water flow manifold structure 68which defines the water inlet 52 and outlet 53 and is sealed by anO-ring seal 69. The sliding mounting 63 for the rear end of the innertube 43 of structure 41 is similarly provided by a ring flange 71fastened to the water manifold structure 68 and is sealed by an O-ringseal 72. An annular piston 73 is located within ring flange 71 andconnected by a screw thread connection 80 to the back end of the innertube 43 of structure 41 so as to close a water inlet manifold chamber 74which receives the incoming flow of cooling from inlet 52. Piston 73slides within hardened surfaces on ring flange 71 and is fitted withO-rings 81, 82. The sliding seal provided by piston 73 not only allowsmovements of the inner tube 43 due to differential thermal expansion ofstructure 41 but it also allows movement of tube 43 to accommodate anymovement of structure 41 generated by excessive water pressure in thecooling jacket. If for any reason the pressure of the cooling water flowbecomes excessive, the outer tube of structure 41 will be forcedoutwardly and piston 73 allows the inner tube to move accordingly torelieve the pressure build up. An interior space 75 between the piston73 and the ring flange 71 is vented through a vent hole 76 to allowmovement of the piston and escape of water leaking past the piston.

The rear part of annular cooling jacket 32 is provided with an outerstiffening pipe 83 part way down the lance and defining an annularcooling water passage 84, through which a separate flow of cooling wateris passed via a water inlet 85 and water outlet 86.

Typically cooling water will be passed through the cooling jacket at aflow rate of 100 m³/hr at a maximum operating pressure of 800 kPa toproduce water flow velocities of 10 meters/minute in the tip region ofthe jacket. The inner and outer parts of the cooling jacket can besubjected to temperature differentials of the order of 200° C. and themovement of tubes 42 and 45 within the sliding mountings 63, 64 can beconsiderable during operation of the lance, but the effectivecross-sectional flow area of the end passage 51 is maintainedsubstantially constant throughout all operating conditions.

It is to be understood that this invention is in no way limited to thedetails of the illustrated construction and that many modifications andvariations will fall within the spirit and scope of the invention.

In that regard it is noted that the oxygen gas injection lance can beintegral with and form part of the upper body of a solids injectionslance.

1. A direct smelting process for producing metals which term includesmetal alloys from a ferrous material which includes the steps of: (a)forming a bath of molten metal and molten slag in a metallurgicalvessel; (b) injecting feed materials being solid material and carriergas into the molten bath at a velocity of at least 40 m/s through adownwardly extending solids injection lance having a delivery tube ofinternal diameter of 40–200 mm that is located so that a central axis ofan outlet end of the lance is at an angle of 20 to 90 degrees to ahorizontal axis and generating a superficial gas flow of at least 0.04Nm³/s/m² within the molten bath (where m² relates to the area of ahorizontal crosssection through the molten bath) at least in part byreactions of injected material in the bath which causes molten materialto be projected upwardly as splashes, droplets and streams and form anexpanded molten bath zone, the gas flow and the upwardly projectedmolten material causing substantial movement of material within themolten bath and strong mixing of the molten bath, the feed materialsbeing selected so that, in an overall sense, the reactions of the feedmaterials in the molten bath are endothermic; and (c) injecting anoxygen-containing gas into an upper region of the vessel via at leastone oxygen gas injection lance and post-combusting combustible gasesreleased from the molten bath, whereby ascending and thereafterdescending molten material in the expanded molten bath zone facilitateheat transfer to the molten bath.
 2. The process defined in claim 1wherein step (b) injecting feed materials into the molten bath so thatthe feed materials penetrate a lower region of the molten bath.
 3. Theprocess defined in claim 1 wherein step (b) includes injecting feedmaterials into the molten bath via the lance at a velocity in the rangeof 80–100 m/s.
 4. The process defined in claim 3 wherein step (b)includes injecting feed materials into the molten bath via the lance ata mass flow rate of up to 2.0 t/m²/s where m² relates to thecross-sectional area of the lance delivery tube.
 5. The process definedin claim 1 wherein step (b) includes injecting feed materials into themolten bath via the lance at a solids/gas ratio of 10–25 kg solids/Nm³gas.
 6. The process defined in claim 5 wherein the solids/gas ratio is10–18 kg solids/Nm³ gas.
 7. The process defined in claim 1 wherein step(b) includes injecting feed materials through a plurality of solidsinjection lances and generating the gas flow of at least 0.04 Nm³/s/m²within the molten bath.
 8. The process defined in claim 1 wherein thegas flow within the molten bath generated in step (b) is at least 0.04Nm³/s/m² at the nominal quiescent surface of the molten bath.
 9. Theprocess defined in claim 8 wherein the gas flow within the molten bathis at a flow rate of at least 0.2 Nm³/s/m².
 10. The process defined inclaim 9 wherein the gas flow rate is at least 0.3 Nm³/s/m².
 11. Theprocess defined in claim 1 wherein the gas flow within the molten bathgenerated in step (b) is less than 2 Nm³/s/m².
 12. The process definedin claim 1 wherein the oxygen-containing gas injected into the moltenbath in step (c) is air or oxygen-enriched air.
 13. The process definedin claim 12 wherein step (c) includes injecting the air oroxygen-enriched air into the vessel at a temperature of 800–1400° C. andat a velocity of 200–600 m/s via at least one oxygen gas injection lanceand forcing the expanded molten bath zone in the region of the lower endof the lance away from the lance and forming a “free” space around thelower end of the lance that has a concentration of molten material thatis lower than the molten material concentration in the expanded moltenbath zone; the lance being located so that: (i) a central axis of thelance is at an angle of 20 to 90° relative to a horizontal axis; (ii)the lance extends into the vessel a distance that is at least the outerdiameter of the lower end of the lance; and (iii) the lower end of thelance is at least 3 times the outer diameter of the lower end of thelance above the quiescent surface of the molten bath.
 14. The processdefined in claim 1 wherein step (c) includes injecting oxygen-containinggas into the vessel in a swirling motion.
 15. The process defined inclaim 1 including controlling the level of dissolved carbon in molteniron to be at least 3 wt % and maintaining the slag in a stronglyreducing condition leading to FeO levels of less than 6 wt %, morepreferably less than 5 wt %, in the slag.
 16. The process defined inclaim 1 including causing molten material to be projected into a topspace above the expanded molten bath zone.
 17. The process defined inclaim 1 wherein step (c) includes post-combusting combustible gasses sothat the level of post-combustion is at least 40%, where post-combustionis defined as:$\frac{\left\lbrack {CO}_{2} \right\rbrack + \left\lbrack {H_{2}O} \right\rbrack}{\left\lbrack {CO}_{2} \right\rbrack + \left\lbrack {H_{2}O} \right\rbrack + \lbrack{CO}\rbrack + \left\lbrack H_{2} \right\rbrack}$where: [CO₂]=volume % of CO₂ in off-gas [H₂O]=volume % of H₂ O inoff-gas [CO]=volume % of CO in off-gas [H₂]=volume % of H₂ in off-gas.